Knife gate valves are used in a variety of applications for quickly shutting off the flow of fluid or other media in a piping system. Typically, knife gate valves have a pair of body members, each formed with a flow passage, fastened together to form a valve body. The body members are spaced apart to provide a seat that accommodates a knife gate when it (the knife gate) is in its closed position, i.e., is operative to shut off flow. Each body member is also formed with an extension and these extensions are also spaced apart to form a housing that accommodates the knife gate in its open position. A knife gate seat arrangement is provided around the flow passages to sealingly engage the knife gate in its closed position and a stuffing box seal arrangement is provided in the housing to sealingly engage the knife gate in both its open and closed positions.
In some of these gate valves, an injectable packing is used to adjust the stuffing box seal as it wears. However, the spacing between the body members provides undesirable leakage paths.
Moreover, in these typical arrangements, routine maintenance is a time consuming and expensive process. Replacement of seals and packing materials requires the removal of the valve from its associated piping system, disassembly and reassembly of the valve and installation in its piping system.